ck_sequence.h

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    1 /*
    2  * Copyright 2010-2015 Samy Al Bahra.
    3  * All rights reserved.
    4  *
    5  * Redistribution and use in source and binary forms, with or without
    6  * modification, are permitted provided that the following conditions
    7  * are met:
    8  * 1. Redistributions of source code must retain the above copyright
    9  *    notice, this list of conditions and the following disclaimer.
   10  * 2. Redistributions in binary form must reproduce the above copyright
   11  *    notice, this list of conditions and the following disclaimer in the
   12  *    documentation and/or other materials provided with the distribution.
   13  *
   14  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
   15  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   16  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   17  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
   18  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   19  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   20  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   21  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   22  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   23  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   24  * SUCH DAMAGE.
   25  */
   26 
   27 #ifndef CK_SEQUENCE_H
   28 #define CK_SEQUENCE_H
   29 
   30 #include <ck_cc.h>
   31 #include <ck_pr.h>
   32 #include <ck_stdbool.h>
   33 
   34 struct ck_sequence {
   35         unsigned int sequence;
   36 };
   37 typedef struct ck_sequence ck_sequence_t;
   38 
   39 #define CK_SEQUENCE_INITIALIZER { .sequence = 0 }
   40 
   41 CK_CC_INLINE static void
   42 ck_sequence_init(struct ck_sequence *sq)
   43 {
   44 
   45         ck_pr_store_uint(&sq->sequence, 0);
   46         return;
   47 }
   48 
   49 CK_CC_INLINE static unsigned int
   50 ck_sequence_read_begin(const struct ck_sequence *sq)
   51 {
   52         unsigned int version;
   53 
   54         for (;;) {
   55                 version = ck_pr_load_uint(&sq->sequence);
   56 
   57                 /*
   58                  * If a sequence is even then associated data may be in a
   59                  * consistent state.
   60                  */
   61                 if (CK_CC_LIKELY((version & 1) == 0))
   62                         break;
   63 
   64                 /*
   65                  * If a sequence is odd then a thread is in the middle of an
   66                  * update. Retry the read to avoid operating on inconsistent
   67                  * data.
   68                  */
   69                 ck_pr_stall();
   70         }
   71 
   72         ck_pr_fence_load();
   73         return version;
   74 }
   75 
   76 CK_CC_INLINE static bool
   77 ck_sequence_read_retry(const struct ck_sequence *sq, unsigned int version)
   78 {
   79 
   80         /*
   81          * If the sequence number was updated then a read should be
   82          * re-attempted.
   83          */
   84         ck_pr_fence_load();
   85         return ck_pr_load_uint(&sq->sequence) != version;
   86 }
   87 
   88 #define CK_SEQUENCE_READ(seqlock, version)                                              \
   89         for (*(version) = 1;                                                            \
   90             (*(version) != 0) && (*(version) = ck_sequence_read_begin(seqlock), 1);     \
   91             *(version) = ck_sequence_read_retry(seqlock, *(version)))
   92 
   93 /*
   94  * This must be called after a successful mutex acquisition.
   95  */
   96 CK_CC_INLINE static void
   97 ck_sequence_write_begin(struct ck_sequence *sq)
   98 {
   99 
  100         /*
  101          * Increment the sequence to an odd number to indicate
  102          * the beginning of a write update.
  103          */
  104         ck_pr_store_uint(&sq->sequence, sq->sequence + 1);
  105         ck_pr_fence_store();
  106         return;
  107 }
  108 
  109 /*
  110  * This must be called before mutex ownership is relinquished.
  111  */
  112 CK_CC_INLINE static void
  113 ck_sequence_write_end(struct ck_sequence *sq)
  114 {
  115 
  116         /*
  117          * Increment the sequence to an even number to indicate
  118          * completion of a write update.
  119          */
  120         ck_pr_fence_store();
  121         ck_pr_store_uint(&sq->sequence, sq->sequence + 1);
  122         return;
  123 }
  124 
  125 #endif /* CK_SEQUENCE_H */

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FreeBSD/Linux Kernel Cross Reference sys/contrib/ck/include/ck_sequence.h

FreeBSD/Linux Kernel Cross Reference
sys/contrib/ck/include/ck_sequence.h